Patent application title: IMAGE FORMING APPARATUS

Abstract:

An image forming apparatus has an improved structure, so that it is able
to clean an ACR sensor in accordance with an ACR operation, and without
requiring a user manipulation. The image forming apparatus includes a
plurality of photosensitive media on which color images are formed
respectively, a transfer unit to receive color images from the plurality
of photosensitive media and transfer the received color images onto a
printing medium, an auto color registration (ACR) unit to perform the ACR
operation with respect to the transferred image, and a cleaning member to
clean the ACR unit in association with the ACR operation.

Claims:

1. An image forming apparatus, comprising:a plurality of photosensitive
media on which color images are formed respectively;a transfer unit to
receive color images from the plurality of photosensitive media and to
transfer the received color images onto a printing medium;an auto color
registration (ACR) unit to perform an ACR operation with respect to the
transferred image; anda cleaning member to clean the ACR unit in
association with the ACR operation.

2. The image forming apparatus of claim 1, wherein the transfer unit
comprises:a first transfer member to receive images being transferred
from the plurality of photosensitive media in an overlapping manner; anda
second transfer member contacting the first transfer member, with the
printing medium interposed therebetween, to transfer a composite form of
the transferred images from the first transfer member onto the printing
medium.

3. The image forming apparatus of claim 2, wherein the ACR unit
comprises:an ACR sensor to sense the composite image on the first
transfer member;a cover member to selectively cover the ACR sensor;a
spacer member to selectively space the first and second transfer members
from each other; anda movable unit to move the cover member and the
spacer member, respectively.

4. The image forming apparatus of claim 3, wherein the cleaning member
operates in association with a covering operation of the cover member.

5. The image forming apparatus of claim 4, wherein the movable unit
comprises:a movable cam rotatably formed between the cover member and the
spacer member; anda driving source to provide the movable cam with a
driving force.

6. The image forming apparatus of claim 5, wherein the movable cam is
rotatable between a non-ACR position where the cover member covers the
ACR sensor and the first and second transfer members contact each other,
and an ACR position where the cover member does not cover the ACR sensor
and the first and second transfer members are spaced away from each
other.

7. The image forming apparatus of claim 6, wherein the cover member
comprises:a guide surface to guide the movable cam.

8. The image forming apparatus of claim 6, wherein the spacer member
comprises:a lever rotatable about a spacer axis by an interaction with
the movable cam, and having the second transfer member supported thereon.

9. The image forming apparatus of claim 8, wherein the cover member is
elastically biased by a first elastic member towards the ACR position,
and the spacer member is elastically biased by a second elastic member
towards the non-ACR position.

10. The image forming apparatus of claim 4, wherein the cleaning member
comprises:an elastic material formed on the cover member.

11. The image forming apparatus of claim 2, wherein:the first transfer
member comprises:a belt supported by a plurality of support rollers to
run; andthe second transfer member comprises:a roller rotating in contact
with the belt.

12. The image forming apparatus of claim 1, further comprising a
controller to control the movable unit so that the ACR unit starts the
ACR operation and the cleaning member starts a cleaning operation
concurrently, after a predetermined number of pages of an image transfer
is performed.

13. An image forming apparatus, comprising:a first, second, third and
fourth (first to fourth) photosensitive media on which color images are
formed respectively;a transfer unit to receive color images from the
first to fourth photosensitive media in an overlapping manner and to
transfer a composite form of the received images onto a printing
medium;an auto color registration (ACR) unit to perform an ACR operation
with respect to the transferred composite image;a cleaning member to
clean the ACR unit in association with the ACR operation; anda controller
to cause the ACR unit to start the ACR operation and the cleaning member
to start the cleaning operation concurrently, after a predetermined
number of pages of an image transfer is performed.

14. The image forming apparatus of claim 13, wherein the transfer unit
comprises:a transfer belt on which images of the first to fourth
photosensitive media are transferred in an overlapping manner; anda
transfer roller contacting the transfer belt, and having the printing
medium interposed therebetween, to transfer a composite form of
transferred images from the transfer belt onto the printing medium.

15. The image forming apparatus of claim 14, wherein the ACR unit
comprises:an ACR sensor to sense the composite image on the first
transfer member;a cover member to selectively cover the ACR sensor;a
spacer member to selectively space the transfer belt and the transfer
roller from each other; anda movable unit, controlled by the controller,
to move the cover member and the spacer member, respectively.

16. The image forming apparatus of claim 15, wherein the cleaning member
operates in association with a covering operation of the cover member.

17. The image forming apparatus of claim 16, wherein the movable unit
comprises:a movable cam rotatably formed between the cover member and the
spacer member; anda driving source, controlled by the controller, to
provide the movable cam with driving forces in different directions.

18. The image forming apparatus of claim 17, wherein the movable cam is
rotatable between a non-ACR position where the cover member covers the
ACR sensor and the transfer belt and the transfer roller contact each
other, and an ACR position where the cover member does not cover the AC
sensor, and the transfer belt and the transfer roller are spaced away
from each other.

19. An image forming apparatus, comprising:an auto color registration
(ACR) unit having an ACR sensor to perform an ACR operation; anda cover
member to move between a closed state in which the cover member covers
the ACR sensor and an open state in which the cover member does not cover
the ACR sensor, the cover member having a cleaning member mounted
thereto;wherein the cleaning member cleans the ACR sensor when the cover
member moves from the closed state to the open state to perform the ACR
operation independent of a user manipulation.

20. A method of cleaning an auto color registration (ACR) sensor in an
image forming apparatus, the method comprising:moving a cover member
having a cleaning member mounted thereto between a closed state in which
the cover member covers the ACR sensor and an open state in which the
cover member does not cover the ACR sensor; andcleaning the ACR sensor
with the cleaning member when the cover member moves from the closed
state to the open state to perform an ACR operation independent of a user
manipulation.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application claims priority under 35 U.S.C. §119(a) from
of Korean Patent Application No. 10-2007-0056246, filed on Jun. 8, 2007,
in the Korean Intellectual Property Office, the disclosure of which is
hereby incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

[0002]1. Field of the Invention

[0003]The present general inventive concept relates to an image forming
apparatus to print a color image onto a printing medium.

[0004]2. Description of the Related Art

[0005]An image forming apparatus such as a printer, copier, facsimile or
multi-function unit that integrates the above functions has a main
function of printing an image onto a printing medium. A color image
forming apparatus is also available, which prints images in multiple
colors.

[0006]A color image forming apparatus generally includes a plurality of
photosensitive media to form electrostatic latent images for color
printing, a plurality of developing units to develop the electrostatic
latent images into developed images in corresponding colors, a transfer
unit to receive the developed color images on one another and transfer a
composite image onto a printing medium, a fusing unit to fix the
transferred image to the printing medium, and a discharge unit to
discharge the printing medium outside.

[0007]The color image forming apparatus carries out auto color
registration (ACR) to align images of each color exactly to intended
locations. By the ACR, it is checked whether the color images are
correctly printed on the printing medium, and if detected, an abnormality
is corrected automatically. Accordingly, an ACR sensor is mounted, facing
the transfer unit to sense the color images transferred onto the transfer
unit.

[0008]The ACR sensor has to be kept clean, in order to perform precise
sensing. In a conventional way, a user cleans the ACR sensor using a
separate cleaning tool, or operates a separate member such as a sensor
cover covering the ACR sensor to wipe contaminants off the ACR sensor.

[0009]The ACR sensor is cleaned only when the user notices that the sensor
is contaminated. Therefore, the ACR sensor is left contaminated and thus
has deterioration of sensing accuracy, if the user does not recognize it.
As a result, a color image forming apparatus has a degradation of image
quality.

SUMMARY OF THE INVENTION

[0010]The present general inventive concept provides an image forming
apparatus of an improved structure, to clean an ACR sensor in association
with an ACR operation, without requiring a separate manipulation by a
user.

[0011]Additional aspects and utilities of the present general inventive
concept will be set forth in part in the description which follows and,
in part, will be obvious from the description, or may be learned by
practice of the general inventive concept.

[0012]The foregoing and other aspects and utilities of the present general
inventive concept may be achieved by providing an image forming
apparatus. The image forming apparatus may include a plurality of
photosensitive media on which color images are formed respectively, a
transfer unit to receive color images from the plurality of
photosensitive media and to transfer the received color images onto a
printing medium, an auto color registration (ACR) unit to perform an ACR
operation with respect to the transferred image, and a cleaning member to
clean the ACR unit in association with the ACR operation.

[0013]The transfer unit may include a first transfer member to receive
images being transferred from the plurality of photosensitive media in an
overlapping manner, and a second transfer member contacting the first
transfer member, with the printing medium interposed therebetween, to
transfer a composite form of the transferred images from the first
transfer member onto the printing medium.

[0014]The ACR unit may include an ACR sensor to sense the composite image
on the first transfer member, a cover member to selectively cover the ACR
sensor, a spacer member to selectively space the first and second
transfer members from each other, and a movable unit to move the cover
member and the spacer member, respectively.

[0015]The movable unit may include a movable cam rotatably formed between
the cover member and the spacer member, and a driving source to provide
the movable cam with a driving force.

[0016]The movable cam may be rotatable between a non-ACR position where
the cover member covers the ACR sensor and the first and second transfer
members contact each other, and an ACR position where the cover member
does not cover the ACR sensor and the first and second transfer members
are spaced away from each other.

[0017]The cover member may include a guide surface to guide the movable
cam.

[0018]The spacer member may be a lever rotatable about a spacer axis by an
interaction with the movable cam, and having the second transfer member
supported thereon.

[0019]The cover member may be elastically biased by a first elastic member
towards the ACR position, and the spacer member may be elastically biased
by a second elastic member towards the non-ACR position.

[0020]The cleaning member may operate in association with the covering
operation of the cover member.

[0021]The cleaning member may be an elastic material formed on the cover
member.

[0022]The first transfer member may be a belt supported by a plurality of
support rollers to run, and the second transfer member may be a roller
rotating in contact with the belt.

[0023]The image forming apparatus may further include a controller to
control the movable unit so that the ACR unit starts an ACR operation and
the cleaning member starts a cleaning operation concurrently, after a
predetermined number of pages of an image transfer is performed.

[0024]The foregoing and other aspects and utilities of the present general
inventive concept may be achieved by providing an image forming
apparatus. The image forming apparatus may include a first, second, third
and fourth (first to fourth) photosensitive media on which color images
are formed respectively, a transfer unit to receive color images from the
first to fourth photosensitive media in an overlapping manner and to
transfer a composite form of the received images onto a printing medium,
an auto color registration (ACR) unit to perform an ACR operation with
respect to the transferred composite image, a cleaning member to clean
the ACR unit in association with the ACR operation, and a controller to
cause the ACR unit to start the ACR operation and the cleaning member to
start the cleaning operation concurrently, after a predetermined number
of pages of an image transfer is performed.

[0025]The foregoing and/or other aspects and utilities of the general
inventive concept may also be achieved by providing an image forming
apparatus including an auto color registration (ACR) unit having an ACR
sensor to perform an ACR operation, and a cover member to move between a
closed state in which the cover member covers the ACR sensor and an open
state in which the cover member does not cover the ACR sensor, the cover
member having a cleaning member mounted thereto, wherein the cleaning
member cleans the ACR sensor when the cover member moves from the closed
state to the open state to perform the ACR operation independent of a
user manipulation.

[0026]The foregoing and/or other aspects and utilities of the general
inventive concept may also be achieved by providing a method of cleaning
an auto color registration (ACR) sensor in an image forming apparatus,
the method including moving a cover member having a cleaning member
mounted thereto between a closed state in which the cover member covers
the ACR sensor and an open state in which the cover member does not cover
the ACR sensor, and cleaning the ACR sensor with the cleaning member when
the cover member moves from the closed state to the open state to perform
an ACR operation independent of a user manipulation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]These and/or other aspects and utilities of the present general
inventive concept will become apparent and more readily appreciated from
the following description of the embodiments, taken in conjunction with
the accompanying drawings of which:

[0028]FIG. 1 is a view illustrating an image forming apparatus according
to an example embodiment of the present general inventive concept;

[0029]FIG. 2 is a cross section view illustrating an auto color
registration (ACR) unit and a cleaning member in a non-ACR position;

[0030]FIG. 3 is a cross section view illustrating an ACR unit and a
cleaning member in an ACR position; and

[0031]FIG. 4 is a flowchart illustrating a method of cleaning an auto
color registration (ACR) sensor in an image forming apparatus according
to an embodiment of the present general inventive concept.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032]Reference will now be made in detail to embodiments of the present
general inventive concept, examples of which are illustrated in the
accompanying drawings, wherein like reference numerals refer to the like
elements throughout. The embodiments are described below in order to
explain the present general inventive concept by referring to the
figures.

[0033]Referring to FIG. 1, an image forming apparatus 1 according to an
example embodiment of the present general inventive concept includes a
first, second, third and fourth (first to fourth) photosensitive media
20, 30, 40, 50, a transfer unit 60, an auto color registration (ACR) unit
70, a cleaning member 80, and a controller 90.

[0034]The first to fourth photosensitive media 20, 30, 40, 50 are arranged
in tandem inside a main body 10 of the image forming apparatus 1, to form
electrostatic latent images of each color by the light exposure of a
light exposure unit 12. When the electrostatic latent images of each
color are formed on the first to fourth photosensitive media 20, 30, 40,
50, the images are developed by first to fourth developing rollers 21,
31, 41, 51, respectively.

[0035]In the following example, the first to fourth photosensitive media
20, 30, 40, 50 are developed to yellow, magenta, cyan and black images.

[0036]Because developing images on the first to fourth photosensitive
media 20, 30, 40, 50 into color images is already well known in the art,
a detailed explanation and drawing will be omitted for the sake of
brevity.

[0037]The main body 10 of the image forming apparatus 1 houses therein and
protects components to print a color image on a printing medium (P),
including, the first to fourth photosensitive media 20, 30, 40, 50, the
transfer unit 60, the ACR unit 70, and the cleaning member 80. A feeding
cassette 11, storing a stack of printing media (P), is removably mounted
in the main body 10, to feed printing media (P) into the main body 10.

[0038]The technical structure of the main body 10 of the image forming
apparatus 1 is generally known, and therefore, a detailed explanation or
drawings thereof will be omitted for the sake of brevity.

[0039]The transfer unit 60 receives color images from the first to fourth
photosensitive media 20, 30, 40, 50 in an overlapping manner, and
transfers a composite image onto the printing medium (P). The transfer
unit 60 includes a transfer belt 62, and a transfer roller 61. The color
image is transferred by a voltage difference. As this is generally known,
a detailed explanation will be omitted for the sake of brevity.

[0040]The transfer belt 62 receives color images in an overlapping manner,
from the first to fourth photosensitive media 20, 30, 40, 50. As the
transfer belt 62 passes through the first to fourth photosensitive media
20, 30, 40, 50, yellow, magenta, cyan and black images are transferred
onto the transfer belt 62 consecutively from the first to fourth
photosensitive media 20, 30, 40, 50. The transfer belt 62 is movably
supported by a plurality of support rollers 61a.

[0041]Although the embodiment explained above has exemplified the transfer
belt 62 as receiving the color images from the first to fourth
photosensitive media 20, 30, 40, 50, this will not be construed as
limiting. Any unit or member that can receive color images from the first
to fourth photosensitive media 20, 30, 40, 50, such as transfer drum or
roller, may be implemented.

[0042]A plurality of rollers 61b are arranged along an inner surface of
the transfer belt 62, corresponding with the first to fourth
photosensitive media 20, 30, 40, 50 arranged on an outer surface of the
transfer belt 62, to help transfer the images from the first to fourth
photosensitive media 20, 30, 40, 50.

[0044]The printing medium (P) bearing the color image passes through the
fusing unit 13, where the image is fixed onto the printing medium (P),
and is discharged out.

[0045]The ACR unit 70 conducts an ACR operation regarding the transferred
image. The ACR operation includes determining whether the color images
are printed onto the printing medium P in alignment with each other, and
if a determination is made that it is not in alignment with each other,
an alignment of the images is corrected automatically. The ACR unit 70
includes an ACR sensor 71, a cover member 72, a spacer member 73, and a
movable unit 74.

[0046]The ACR sensor 71 senses the image transferred onto the transfer
belt 62. The ACR sensor 71 is mounted in the main body 10, facing the
transfer belt 62, to sense a final form of the composite color image on
the transfer belt 62.

[0047]The ACR sensor 71 is arranged behind the first to fourth
photosensitive media 20, 30, 40, 50, in an advancing direction of the
transfer belt 62. The image is not transferred onto the printing medium
(P) during the ACR operation, that is, while the ACR sensor 71 performs a
sensing operation.

[0048]Although not illustrated, two or more ACR sensors 71 can be arranged
opposite to each other in a width direction, to detect the composite
image on the transfer belt 62 accurately.

[0049]The ACR sensor 71 may be implemented as an optical sensor having a
high detection ability, such as a photo transistor, photo diode, or the
like, to detect the alignment of the images with accuracy. Because use of
the optical sensor is generally known, a detailed explanation or drawings
thereof will be omitted for the sake of brevity.

[0050]Referring to FIGS. 2 and 3, the cover member 72 is rotatable about a
cover axis 72a, to selectively cover the ACR sensor 71. The cover member
72 is rotatable between a cover position to cover the ACR sensor 71 in a
non-ACR operation, and an open position to open the ACR sensor to start
the ACR operation.

[0051]The cover member 72 is elastically supported by a first elastic
member 72b. The elastic member 72b may be implemented as a compression
coil spring, whose one end is supported on the main body 10 of the image
forming apparatus 1, and an other end supports the cover member 72. The
elastic member 72b elastically biases the cover member 72 towards the ACR
sensor open position.

[0052]Although the present embodiment implemented a compression coil
spring as the first elastic member 72b to support the cover member 72,
this should not be construed as limiting. Any elastic unit or member such
as a torsion spring, that is capable of elastically urging the cover
member 72 to the ACR sensor 71, can be used as the first elastic member
72b.

[0053]The spacer member 73 selectively distances the transfer belt 62 away
from the transfer roller 61 to perform the ACR operation. The spacer
member 73 may be implemented as a lever, rotating about a spacer axis
73a, while supporting the transfer roller 61.

[0054]The spacer member 73 is elastically urged by the second elastic
member 73b towards the position where the transfer belt 62 contacts the
transfer roller 61. Referring to FIGS. 2 and 3, the second elastic member
73b may be implemented as a compression coil spring whose one end is
supported on the main body 10 of the image forming apparatus 1, while an
other end is supported on the spacer member 73. The second elastic member
73b biases the spacer member 73 to return towards an original position,
to cause the transfer roller 61 to move from a position distanced away
from the transfer belt 62 to a position contacting the transfer belt 62
(FIG. 2).

[0055]The second elastic member 73b may be a compression coil spring, like
the first elastic member 72b. However, one skilled in the art will
appreciate that any other elastic unit or member such as torsion spring
can be used as the second elastic member 73b without departing from the
scope of the general inventive concept.

[0056]The movable unit 74 moves the cover member 72 and the spacer member
73. The movable unit 74 includes a movable cam 75 and a driving source
76.

[0057]The movable cam 75 is disposed between the cover member 72 and the
spacer member 73, to rotate about a movable axis 75a. The movable axis
75a is eccentrically formed with respect to the movable cam 75.

[0058]The movable cam 75 is rotated between a non-ACR position where the
cover member 72 covers the ACR sensor 71 and the transfer roller 61
contacts the transfer belt 62 to carry out a transfer operation, and an
ACR position where the ACR sensor 71 is not covered by the cover member
72 and can perform an ACR operation and the transfer roller 61 is spaced
apart from the transfer belt 62.

[0059]According to movement of the movable cam 75 towards the non-ACR
position, as illustrated in FIG. 2, the cover member 72 moves to the
cover position, and the spacer member 73 is positioned at a contact
position. Then according to the movement of the movable cam 75 towards
the ACR position, as illustrated in FIG. 3, the cover member 72 moves to
the open position, and the spacer member 73 moves to the spacing
position. That is, the movable cam 75 moving towards the non-ACR
position, the cover member 72 moving towards the cover position, and the
spacer member 73 moving towards the contact position, happen
concurrently. Likewise, the movable cam 75 moving towards the ACR
position, the cover member 72 moving towards the open position, and the
spacer member 73 moving towards the spacing position, also happen
concurrently.

[0060]A guide surface 72c is formed on the cover member 72, to guide a
covering operation of the cover member 72 according to the movable cam
75. The cover member 72 has a space formed therein to selectively receive
the ACR sensor 71, and the guide surface 72c formed on an outer surface
thereof to contact the movable cam 75.

[0061]Referring to FIGS. 2 and 3, the driving source 76 provides a driving
force so that the movable cam 75 can be driven in different directions
(R1, R4). The controller 90, which will be explained below, controls the
driving directions of the driving source 76.

[0062]The cleaning member 80 cleans the ACR sensor 71 of the ACR unit 70,
in association with the ACR operation of the ACR unit 70. The cleaning
member 80 is formed on an inner side of the cover member 72 to be moved
in association with a rotational movement of the cover member 72. The
cleaning member 80 may be implemented as an elastic material such as a
sponge.

[0063]The cleaning member 80 may be attached to the inner side of the
cover member 72, to clean the sensing surface of the ACR sensor 71 that
faces the transfer belt 62. When the covering member 72 is in the cover
position, that is, when the covering member 72 is in the non-ACR position
to cover the ACR sensor 71, the cleaning member 80 contacts the sensing
surface of the ACR sensor 71 to protect the ACR sensor 71 from external
contaminants.

[0064]When the cover member 72 is in an open position, that is, when the
cover member 72 is in the ACR position so that the cover member 72 does
not cover the ACR sensor 71 so that the ACR sensor can perform the ACR
operation, the cleaning member 80 wipes contaminants off the sensing
surface of the ACR sensor 71 in association with an opening of the cover
member 72.

[0065]As the cover member 72 returns to the non-ACR position (cover
position) upon completing the ACR operation, the cleaning member 80 again
wipes off the sensing surface of the ACR sensor 71.

[0066]The controller 90 controls the components of the image forming
apparatus 1 throughout the printing process. In the present embodiment,
the controller 90 particularly controls the ACR operation of the ACR unit
70, and the cleaning operation of the cleaning member 80.

[0067]More particularly, the controller 90 controls the driving direction
of the driving source 76 for the ACR operation to start with the printing
operation, or to start after the printing media (P) on which the color
images are transferred exceeds a predetermined number of counts, such as
200 sheets.

[0068]As the movable cam 75 rotates in an R4 direction (FIG. 3), the cover
member 72 rotates in R5 direction, thereby not obstructing the ACR sensor
71 and also concurrently rotating the spacer member 73 in an R6 direction
to the ACR position where the transfer belt 62 and the transfer roller 61
are spaced away from each other.

[0069]The driving source 76, under control of the controller 90, rotates
the movable cam 75 in the direction R1 in the transfer operation, so that
the cover member 72 and the spacer member 73 are rotated about the cover
axis 72a and the spacer axis 73a in R2 and R3 directions, respectively,
and stop at the non-ACR position.

[0070]The cleaning member 80 cleans the ACR sensor 71 in accordance with
the rotation of the cover member 72 in R2 and R5 directions.

[0071]The controller 90 is connected with the ACR sensor 71 to provide a
signal exchange, and therefore, is capable of determining whether color
images are in alignment with each other from the signal received from the
ACR sensor 71. On detecting a signal corresponding to misalignment of the
color images, the controller 90 starts a compensation process to align
the images.

[0072]The operation of the image forming apparatus constructed as
explained above according to the present embodiment will be explained
below with reference to FIGS. 1 to 3.

[0073]Referring to FIGS. 1 and 2, electrostatic latent images on the first
to fourth photosensitive media 20, 30, 40, 50 are developed to yellow,
magenta, cyan and black images by the first to fourth developing rollers
21, 31, 41, 51, respectively. The developed color images are then
contacted with the first to fourth photosensitive media 20, 30, 40, 50,
and transferred onto the transfer belt 62 in an overlapping manner.

[0074]Referring to FIG. 2, as the movable cam 75 is moved in the R1
direction, the cover member 72 and the spacer member 73 are moved to the
non-ACR position. Accordingly, the cover member 72 covers the ACR sensor
71, and the transfer belt 62 and the transfer roller 61 contact each
other. The cleaning member 80 of the cover member 72 screens the sensing
surface of the ACR sensor 71, thereby protecting the ACR sensor 71 from
external contaminants.

[0075]The composite image is transferred from the transfer belt 62 onto a
printing medium (P) passing in between the transfer belt 62 and the
transfer roller 61, and fixed to the printing medium (P) by the fusing
unit 13. The printing medium (P) with the fixed color image is then
discharged out of the main body 10 of the image forming apparatus 1.

[0076]Meanwhile, the controller 90 may control the ACR unit 70 to start
the ACR operation when a predetermined number of pages are printed.
Accordingly, as illustrated in FIG. 3, the driving source 76 causes the
movable cam 75 to rotate about the movable axis 75a in the R4 direction.
The movable cam 75 is guided along the guide surface 72c formed on the
outer side of the cover member 72, and the cover member 72 is elastically
biased towards the ACR position by the first elastic member 72b. As a
result, the cover member 72 rotates in the R5 direction, and stops at the
ACR position (open position).

[0077]The movable cam 75 rotating in the R4 direction interferes with the
spacer member 73, and thus causes the spacer member 73 to rotate about
the spacer axis 73a in the R6 direction. As a result, the second elastic
member 73b is compressed against the spacer member 73, and the transfer
roller 61, being supported by the spacer member 73, is spaced away from
the transfer belt 62.

[0078]Accordingly, the sensing surface of the ACR sensor 71 is open, to
sense the composite image formed on the transfer belt 62. The cleaning
member 80, which is brought in contact with the ACR sensor 71 by the
rotation of the cover member 72 in the R5 direction, rotates along with
the cover member 72, to wipe off the sensing surface of the ACR sensor
71.

[0079]The information based on the sensing of the composite color image by
the ACR sensor 71 is transmitted to the controller 90, and the controller
90 determines whether color images are in alignment with each other based
on the received information. If an abnormality in the image alignment is
detected, the controller 90 causes a compensation process to start.

[0080]If no abnormality in the image alignment is detected, the controller
90 resumes the printing operation. Accordingly, the controller 90 causes
the driving direction of the driving source 76 to change to the R1
direction as illustrated in FIG. 2, so that the cover member 72 and the
spacer member 73 rotate in the R2 and R3 directions, respectively, and
stop at the non-ACR position. At this time, the cleaning member 80 wipes
off the sensing surface of the ACR sensor 71 once again in accordance
with the rotation of the cover member 72, before the ACR sensor 71 is
covered.

[0081]In the non-limiting examples set forth above, the ACR operation
starts after a predetermined number of pages are printed. However, one
skilled in the art will appreciate that other variations and
modifications are possible. By way of a few examples of such
modifications, the ACR operation may start before the initial printing
process, or start regularly after each printing operation.

[0082]FIG. 4 is a flowchart illustrating a method of cleaning an auto
color registration (ACR) sensor in an image forming apparatus according
to an embodiment of the present general inventive concept. Referring to
FIG. 4, in operation 410, a cover member having a cleaning member mounted
thereto is moved between a closed state in which the cover member covers
the ACR sensor and an open state in which the cover member does not cover
the ACR sensor. In operation 420, the ACR sensor is cleaned with the
cleaning member when the cover member moves from the closed state to the
open state to perform an ACR operation independent of a user
manipulation.

[0083]The present general inventive concept can also be embodied as
computer-readable codes on a computer-readable medium. The
computer-readable medium can include a computer-readable recording medium
and a computer-readable transmission medium. The computer-readable
recording medium is any data storage device that can store data that can
be thereafter read by a computer system. Examples of the
computer-readable recording medium include read-only memory (ROM),
random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, and
optical data storage devices. The computer-readable recording medium can
also be distributed over network coupled computer systems so that the
computer-readable code is stored and executed in a distributed fashion.
The computer-readable transmission medium can transmit carrier waves or
signals (e.g., wired or wireless data transmission through the Internet).
Also, functional programs, codes, and code segments to accomplish the
present general inventive concept can be easily construed by programmers
skilled in the art to which the present general inventive concept
pertains.

[0084]As explained above, according to various embodiments of present
general inventive concept, both the cover member 72 to cover the ACR
sensor 71 and having the cleaning member 80 therein, and the spacer
member 73 to support the transfer roller 61, can be moved concurrently to
the non-ACR position or to the ACR position, by covering the ACR sensor
71 according to a direction of the movable unit 74. As a result, the ACR
sensor is cleaned and the transfer roller 61 is spaced apart from the
transfer belt 62, in association with the ACR operation, and without
requiring a separate manipulation by a user.

[0085]Because the ACR sensor 71 cleaning and ACR operation are performed
concurrently and require a simple structure, a more economical and
compact image forming apparatus is provided. Furthermore, because the ACR
sensor 71 is cleaned every time the ACR operation is done, efficiency of
the ACR operation increases.

[0086]Although various embodiments of the present general inventive
concept have been illustrated and described, it will be appreciated by
those skilled in the art that changes may be made in these embodiments
without departing from the principles and spirit of the general inventive
concept, the scope of which is defined in the appended claims and their
equivalents.